U.S. patent application No. 639,163 filed Aug. 9, 1984, now U.S. Pat. No. 4,671,445, of which this application is a Continuation in Part, describes staplers adapted for use in stapling together layers of living tissues that have a flexible spine structure between a head assembly in which the staples to be applied are carried, and an actuator assembly that can be manually actuated to apply the staples from the head assembly. That flexible spine structure affords orienting the head and actuator assemblies at different positions relative to each other, which can facilitate using the stapler assembly in certain types of operations.